Module
What's known as plugin or addon in other platforms, is what we call a module in the Drupal universe. Drupal core itself is a a collection of modules as well and the community has added and maintains tens of thousands of individual modules on top of that.
The User hash module allows you to create an individual hash for each user. Use it as a light-weight user identification where you do not want to use the Drupal login credentials. E.g.